CODEWITHSUNDEEP
c++exceptionconstructor
Santosh Kantharaj
Santosh Kantharaj

Reputation: 161

Strange format for throwing exception from a constructor

Our professor gave us a shell to make a program in. In it he gave us a class called "Maker", and it is capable of throwing exceptions. I'm confused about how to throw and catch the error, given the format of the constructor that he has provided.

He gave us his own special exception header file called CycleFoundException.h, which looks like this:

#include <iostream>
#include <exception>

using namespace std;

class CycleFoundException: public exception {
  // Don't add code
};

Here is the Maker.h header file:

#include "CycleFoundException.h"    

class Maker
{
 private:
  // insert instance variables

 public:
  Maker(int x) throw (CycleFoundException);
};

And finally the cpp shell, Maker.cpp: 

#include Maker.h

Maker::Maker(int x) throw (CycleFoundException){
//add code here
}

int main()
{
    return 0;
}

I've never seen a constructor declaration like this. Why is the "throw (CycleFoundException)" be tagged onto the declaration of the constructor? Is that necessary?

And how would I throw an exception given this format? Would I still do it the same way I would otherwise, aka if a certain condition is not met then throw the exception (from within the body of the constructor)? Thanks.

Upvotes: 1

Views: 130

Answers (1)

Nikos C.
Nikos C.

Reputation: 51832

This is simply a way to say what kinds of exceptions a function is allowed to throw:

Maker::Maker(int x) throw (CycleFoundException)

means that Maker::Maker(int) is only allowed to throw CycleFoundException exceptions, nothing else. This is called an "exception specification."

Note that the C++ standard has deprecated this mechanism. It should not be used anymore. You should probably inform your professor about it ;-) They were always problematic: http://mu2e.fnal.gov/public/hep/computing/standards/C++FAQ.shtml#exceptionspec

Upvotes: 2

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